20080519

Efficient pulsed gates for an oscillator stabilized Josephson qubit IBM Watson In arXiv 0709.1478 and New J. Phys.10033027 (2008), Koch, DiVincenzo, Brito and Steffen derive operational specifications for high-fidelity one and two-qubit pulsed gates for a superconducting flux qubit, calculating the Hamiltonian with tunable interaction from initialization to readout.

"The quantitative fact that the values of gate inﬁdelity are at the 1% level – and below – is the major result of this paper."

So, can a "debugged" IBM qubit be used soon for universal quantum computation?

"The short answer is, in our opinion, ultimately yes."

"The answer would certainly be no if the noise threshold for fault-tolerant quantum computation were in the neighborhood of the oft-quoted value of 10−5. It is not inconceivable for the experiment to get to these values someday, since we ﬁnd that the inﬁdelities decrease much faster than linearly with the assumed noise levels."

"To get to 10−5, we would need to get to the very daunting levels of 100nΦ0 at 1Hz for the 1/f noise amplitudes and 100 f s for timing accuracies; there is optimism that both of these numbers are ultimately attainable. Fortunately, while 10−5 was the threshold as it was understood ten years ago, much recent work shows that with good designs, much higher thresholds are possible. According to Terhal and Burkard – 1% is, in fact, on the high end of the noise levels for which fault tolerance may be possible."

"According to the laws of physics, it is particularly difficult to pass light through a hole smaller than half the wavelength of the light used." The Delft group conducted experiments using extremely high time-resolution measurements in the terahertz (THz) frequency range. The group discovered that even if the hole is up to fifty times smaller than the wavelength used, sufficient light can pass through to allow measurements near the hole – an extremely difficult task using other methods. "Improving the sharpness of THz microscopes, coupled with more sensitive detectors, will improve the viability of creating images of biological cells using this type of measurement."

Prior experiments at Leiden University (Nature418, 304-306) have also studied photon transmission through sub-wavelength metal films and shown entanglement conservation to be much more robust than expected – surviving the conversion process from surface-plasmon waves, which tunnel through the barrier, before reradiating as photons on the opposite side of the film. "It's a good omen, because it's saying quantum entanglement can survive when you might not expect it to," says Bill Barnes, a photonics expert at the University of Exeter. "If they can survive this, what else can they survive?"

20080508

Time Reversal in Bose-Einstein Condensates Toulouse | CNRS In arXiv 0804.3514, Martin, Georgeot, and Shepelyansky of Quantware MIPS Center investigate time reversibility in Bose-Einstein condensates (BEC). "We show that inside the regime of quantum chaos, time-reversal dynamics can be inverted from explosion to collapse. The accuracy of time reversal decreases with the increase of atom interactions inside BEC, until it is completely lost – though, surprisingly, quantum chaos helps to restore time reversibility. Existing experimental setups similar to Ryu, Behinaein, and Wayper can test the fundamental question of BEC time reversal discussed here."

20080506

DARPA INFOSEC Mandate DARPA | EOP | Congress In Wired briefing 01 May 2008, Danger Room reports on the new DARPA Information Security program mandated by Congress and ratified by the President. The UNISCA First Committee INFOSEC Chair briefing to the UN General Assembly is particularly àpropos to the initiative. "The Defense Advanced Research Projects Agency, or DARPA, was created 50 years ago in response to the Soviets' launch of Sputnik. In less than a year, DARPA put together the infrastructure that guided the American space effort for decades to come. Now, DARPA has been given new marching orders: to help America fight and win battles online.

Under a directive signed by the President – and recently approved by Congress – nearly every arm of the government's security apparatus is starting work on a massive national cybersecurity initiative designed to protect the United States from electronic attack and strike at adversaries online. DARPA's role: to create a cyberwarfare range where all these new forms of electronic combat can be tried out. According to a defense official familiar with the program, "Congress has given DARPA a direct order; that's only happened once before – with the Sputnik program in the '50s."

Danger Room's sister blog, Threat Level, has a good writeup of the cybersecurity initiative, which has been labeled as a Manhattan Project-type effort. In the case of cybersecurity, there is at least talk of big money: about $30 billion dollars. For its part, DARPA's "National Cyber Range" would create a virtual environment where the Defense Department can mock real warfare, both defense and offense.

DARPA today issued an announcement, describing how the range would be a test where the government could conduct unbiased, quantitative and qualitative assessment of information assurance and survivability tools in a representative network environment ; replicate complex, large-scale, heterogeneous networks and users in current and future Department of Defense (DoD) weapon systems and operations ; enable multiple, independent, simultaneous experiments on the same infrastructure ; enable realistic testing of Internet/Global-Information-Grid (GIG) scale research ; develop and deploy revolutionary cyber testing capabilities, and enable the use of the scientific method for rigorous cyber testing.

This is clearly a serious deal for the agency: DARPA Director Tony Tether is a scheduled speaker at the proposers' day workshop scheduled for mid-May, and apparently plans to help handpick the contractors. Tether is known for his close involvement in DARPA contracts. Many of the details surrounding this program will be classified."